VIDEO: OTEC technology
Ocean Thermal Energy Conversion (OTEC) is a marine renewable energy technology that generates electricity using the solar energy absorbed by the oceans.
The surface water of the ocean is heated by the sun more quickly than the deep ocean water – creating naturally available temperature gradient, or thermal energy.
In geographical areas with warm surface water and cold deep water, the temperature difference can be used to drive a steam cycle – warm surface water passes through a heat exchanger, vaporizing a low boiling point working fluid, usually ammonia, to drive a turbine generator.
The vapor is then cooled by the cold deep ocean water. This condenses the working fluid, turning it back to liquid, so that it can be used again.
The usual difference in the temperature between the surface and deep ocean waters is around 20°C.
OTEC technology is most suitable for the equatorial areas.
There are three kinds of OTEC systems: closed-cycle, open-cycle, and hybrid.
Closed-cycle systems use fluids with a low boiling point, such as ammonia, to rotate a turbine to generate electricity. Warm surface seawater is pumped through a heat exchanger, where ammonia is vaporized. The vapor turns the turbine, powering the generator, and after that it is cooled by the cold deep ocean water.
Open-cycle systems use the tropical oceans’ warm surface water to make electricity, placing warm seawater in low-pressure container, what makes the water boil. The expanding steam drives a low-pressure turbine attached to an electrical generator. The process creates fresh water, because the salt is left in the low-pressure container. The cold water from deep ocean condenses the vapor back to its liquid state.
In a hybrid system, warm seawater enters a vacuum chamber, where it is evaporated into steam, similar to the open-cycle evaporation process. The steam then vaporizes a low boiling point fluid (in a closed-cycle loop) that drives a turbine to produce electricity.
The world’s largest OTEC plant is being designed by Lockheed Martin, in collaboration with Reignwood Group, and the estimated capacity of this plant amounts to 10 MW. Once built, the plant will be deployed off the coast of southern China.
Take a look at the video explaining the principles behind OTEC technology, and Lockheed Martin’s OTEC platform system.